Police and public safety personnel, as well as private organizations, often rely on wireless mobile and portable radios to convey voice and data in an efficient, reliable manner. Much of this communication occurs on open, clear, unencrypted channels. Open communications, however, are subject to eavesdropping and other interference and at times it is necessary to limit the information exchanged to a select group or individual. To this end, secure methods of communications are necessary. Secure communication systems for mobile and portable radios are well known.
Secure communication is possible by encrypting the audio, visual, and/or data (“transmission”) that is transmitted. Encryption keys are used to encrypt the transmission. Communication units having identical encryption keys, i.e. symmetric encryption keys, and encryption algorithms are capable of forming and decoding encrypted transmissions.
A communication unit may be provided with a set or multiple sets of keys to allow practical key management. The set of encryption keys may be referred to as a Cryptogroup, as is known in the Trans-European Trunked Radio service (TETRA) system, or as a Storage Location Number, as is known in the Association of Public Safety Communication Officers (APCO) Project 25 system defined by the Association of Public-Safety Communications Officials, and may also include other key management groups or systems now known or hereafter created that describes a key or a set of encryption keys.
The communication unit is assigned a key within the set of keys for transmissions, but may use any of the keys within the set of keys used for that transmission for reception. This allows the keys within the set to be changed over time, and new keys assigned for transmission in a communication unit without loss of communication with other communication units that may receive newly assigned keys at slightly different times. A set of keys may contain only one encryption key, or may contain more, with typical numbers of encryption keys being two or three. For simplicity, single as well as groups of encryption keys hereafter will be referred to as “encryption keys” or “key” and understood to incorporate both individual as well as sets or groups of keys.
Each individual communication unit may have more than one encryption key. For example, it is frequently desirable for supervisory radios to have several different encryption keys to communicate with different groups of users, each having different encryption keys. In this instance, multiple encryption keys allow the supervisory radio to have secured communications with different groups of users who each may have different encryption keys. Keys may be associated with the addresses of different groups or users to determine which key a user should use when initiating a transmission. A key may be designated ‘default’ for use where no other specific key has been associated with an address.
There are concerns, however, when a receiving communication unit has multiple encryption keys. The receiving communication unit must first validate the transmitting communication unit of the transmission to verify that it is from a trusted source. Currently, the receiving communication unit validates the transmission by one of two methods. In the first method, the receiving communication unit validates the transmission using a particular group of keys provisioned in the receiving communication unit. The transmissions received are limited to the group the receiving communication unit searches. If a transmission is received that is from a communication unit using a key outside the set searched, the transmission is not processed. In the second method, the receiving communication unit validates the transmission against all encryption keys with which it has been provisioned. This method, however, opens the receiving communication unit to spoofing attacks by unauthorized communication units.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not often depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will be understood that the terms and expressions are used with respect to their corresponding respective areas of inquiry and study except where specific meaning have otherwise been set forth herein.